Semiconducting floor covering

ABSTRACT

A semiconducting floor covering which consists of a layer ( 2 ) of conductive material parallel to the surface of the covering and at least one layer ( 1, 3 ) of polyvinyl chloride based material adhered to the layer of conductive material. As plasticizer for the polyvinyl chloride in the floor covering, 2-ethyl hexyl diphenyl phosphate and aliphatic ester compound has been used or these two combined so that per 100 parts of polyvinyl chloride it contains 39-80 parts of plasticizer. It further contains 1-250 parts of talc and/or ATH as filler.

[0001] The present invention relates to a semiconducting floor coveringwhich consists of a layer of conductive material parallel to the surfaceof the covering and at least one layer of polyvinyl chloride basedmaterial which is adhered to the layer of conductive material and whichcontains polyvinyl chloride and at least one plasticizer.

[0002] Semiconducting floor coverings are required in places whereelectrostatic discharges or accumulations cannot be allowed on groundsof safety. This fact concerns e.g. the explosives and computerindustries, and many other places where accumulations of staticelectricity and discharges thereof may cause problems concerning safetyor cost.

[0003] A semiconducting floor covering is understood to be material inwhich resistivity measured from the surface of the covering material tothe grounding point is at least 50 kΩ and no more than 100 MΩ.

[0004] In prior art. a semiconducting floor covering is made of eitherrubber or plastic by adding thereto a sufficient amount of carbon blackby means of which conductivity values assigned to a semiconductingcovering material can be achieved. in another prior art solution thelower layer of a mat is of conductive material on top of which there isprovided an isolating layer of material through which connections havebeen arranged made of conductive material so that the conductivematerial at these points extends from the surface of the coatingmaterial to the bottom. Such a solution is known e.g. from the U.S. Pat.No. 5,307,233 in which chips have been placed on a conductive bottomlayer, the vertical edges of the chips having been coated by conductivematerial.

[0005] A problem with materials containing carbon black is that thematerial normally turns out black, and it cannot be covered with anycolouring material. Further, the use of carbon black makes the machinerydirty during the manufacturing and causes output being wasted e.g. whenchanging the type of material. In addition, stretching such material inmelted conditions deteriorates its conductivity. The solutions involvingconductive elements of various kinds share the drawback that assemblinga mat material from such elements is difficult and expensive, andfurthermore, coating and measuring conductive elements for properoperation is difficult.

[0006] In addition, employing other conductive materials, such as metalparticles, is expensive in such a covering, and further, the use of suchadditives causes significant restrictions to the colours or choosing ofcolours for the material because, due to the conducting properties, thecoverings cannot be coloured and no surface pattern can be printed onthem.

[0007] It is the object of the present invention to provide asemiconducting floor covering by means of which the prior art drawbacksmay be avoided and by means of which floor coverings may be producedthat work well and are wear-resistant, and which may be coloured andpatterned by printing technique, and which may additionally have acolourless or transparent wear-resistant surface layer.

[0008] The floor covering according to the invention is characterized inthat the plasticizer at least mainly consists of 2-ethyl hexyl diphenylphosphate and/or an aliphatic ester compound, and that the polyvinylchloride material contains, as filler, talc and/or aluminium trihydrateso that the relative proportions of the components in the polyvinylchloride material per 100 parts of polyvinyl chloride are 30-80 parts ofsaid plasticizer and 1-250 parts of said filler.

[0009] The essential idea of the invention is that the principalplasticizer used for the polyvinyl chloride material (from hereafter,PVC) is 2-ethyl hexyl diphenyl phosphate (from hereafter, DPOF) and/oran aliphatic ester compound. whereby it is additionally possible toemploy one or more of the following plasticizers:

[0010] monomeric or polymeric phthalates

[0011] monomeric or polymeric adipates

[0012] phosphate plasticizers

[0013] benzoate plasticizers

[0014] polyester plasticizers

[0015] trimellitate plasticizers

[0016] alkylsulphonic acid esters

[0017] polyglycoates

[0018] so that 30-80 parts of plasticizer in all have been used per 100parts of PVC. This means that the proportion of DPOF and/or aliphaticester compound is at least 30 parts per 100 parts of PVC, and theproportion of other plasticizer may vary. Furthermore, an essentialfeature of the invention is that, in addition to plasticizer. fillerwhich contains talc or aluminum hydrate (from hereafter, ATH) has beenadded into the PVC material to such an extent that the proportion ofpure talc or ATH per 100 parts of PVC is 1-250 parts. According to thepreferred embodiment of the invention, it is possible to producecolourless or even transparent PVC whose conductivity continues tofulfill the requirements of a semiconducting material. Yet anotheressential idea of the invention is to have a conductive layer to which aPVC layer has been adhered so that the conductive layer is either thebottommost layer of the floor covering or advantageously close to itsbottom surface.

[0019] The inventive floor covering provides the advantage that theactual floor covering may be produced by simply mixing the materials inquestion to each other in said proportion, after which it may be adheredto the conductive layer either to one or both sides thereof. Byemploying a suitable carbon-glass fiber layer, or a metal layer, theconductive layer may be arranged within the actual covering material asdesired. It is further advantageous of the covering according to theinvention provides that by forming e.g. two PVC layers, the lower ofwhich being coloured, for example white, and a colourless or transparenttop layer, it is possible to produce floor coverings of any desiredcolours, in which the top layer may further be provided withwear-resistant components without degrading its semiconductingproperties.

[0020] In the following, the invention will be described in closerdetail with reference to the accompanying drawings, in which

[0021]FIG. 1 shows an embodiment according to the invention, and

[0022]FIG. 2 shows a second embodiment of the floor covering accordingto the invention.

[0023]FIG. 1 is a schematic representation of a floor covering preparedaccording to the invention. The floor covering consists of PVC material1 which is substantially homogenous. Within the PVC material there isprovided a carbon-glass fiber layer 2, which in this embodiment is theconductive layer. The PVC material 1 consists of PVC, plasticizer andfiller as follows:

EXAMPLE 1

[0024] A 2 mm thick semiconducting material was prepared by mixing 100parts of PVC, with 30 parts of aliphatic ester as plasticizer (tradename Bisoflex 124™, produced by International Specialty Chemicals). 5parts of aluminum trihydrate, i.e. ATH, and 2 parts of titanium dioxide,and 2 parts of stabilizer. Within the layer, a carbon-glass fiber layerwas provided, containing 10% of carbon. The resistivity of the materialwas measured across its thickness in accordance with the standard SFS-EN100015 at 500VDC, and the resistivity obtained was 5×10⁵ Ω.

[0025] This mixture provides a conductivity of 5×10⁵ Ω for PVC materialwith the thickness of 0.1-2 mm. By varying the amounts of plasticizerand filler within the range 30-80 parts of plasticizer and 10-200 partsof filler, the resistivity varies to some degree but remains within thesemiconducting range. The stabilizers are tin, calcium zinc or bariumcalcium zinc based compounds that are commonly used for stabilizing PVCbased materials. These are known per se, and therefore there is no needto describe them any further.

[0026] The PVC material 1 may also be produced as follows:

EXAMPLE 2

[0027] A 1 mm thick semiconducting material was prepared with acarbon-glass fiber layer in the middle, the layer containing 10% ofcarbon as follows:

[0028] 100 parts of PVC, 80 parts of plasticizer (consisting of 40 partsof DPOF, 30 parts of aliphatic ester and 10 parts of di-isodecyl adipate[DIDA]), 202 parts of filler (50 parts of talc and 150 parts of ATH, aswell as 2 parts of titanium dioxide), and 2 parts of stabilizer weremixed. The resistivity of the material was measured across its thicknessin accordance with the standard SFS-EN 100015, and the resistivity of7×10⁵ Ω was obtained.

[0029] Similarly in this manner, different values of resistivity may beobtained within the semiconducting range by varying the amounts ofplasticizer and filler.

[0030] The carbon-glass fiber layer 2 contains 1-50% of carbon, wherebyit forms a layer conductive enough and having adequate strength for useas a floor covering. Instead of the carbon-glass fiber layer, e.g. athin wire mesh may be used which meets the required conductivity values.

[0031]FIG. 2 shows a second embodiment for the floor covering accordingto the invention. In this embodiment, the conductive layer 2 isbottommost. on top of which there is a first PVC layer 1. On top of thefirst PVC layer 1 there is a second PVC layer 3, which deviates from thefirst PVC layer as to its composition and properties. in thisembodiment, the second PVC layer 3 is formed as follows:

EXAMPLE 3

[0032] The material according to Example 1 (thickness 1 mm, without thecarbon-glass fiber layer, layer 1 according to FIG. 2) was adhered to a1 mm thick, colouriess layer prepared as follows (layer 3 according toFIG. 2):

[0033] 100 parts of PVC, 60 parts of plasticizer (DPOF, trade nameSANTICIZER 141), 10 parts of filler (talc) and 2 parts of stabilizer(trade name LANCRO BT 295). A conductive carbon-glass fiber layer wasadhered to the bottom of the layer 1 in FIG. 2, the conductive layercontaining 10% of carbon fiber, the resistivity of the material wasmeasured across its thickness according to the standard SFS-EN 100015,and the resistivity of 17×10⁶ Ω was obtained.

[0034] In this manner, a product has been obtained wherein the secondPVC layer 3 is colourless whereas the first PVC layer 1 is in one way oranother coloured. If desired, the first PVC layer may either be colouredplain or in a way known per se to comprise different patterns or colourswithout causing any substantial changes in its conductivity.Consequently, by incorporating into the second PVC layer 3 componentthat makes it harder and wear-resistant, such as ATH or talc and ifdesired also 1-90 parts of glass in case the proportion of PVC is 100parts, a colourless wear-resistant layer will be obtained through whichthe colours of the first PVC layer can be seen. The conductivity of theentire floor covering will nevertheless stay semiconducting through thelayers 3 and 1 to the conductive layer 2, as desired. If it is desiredthat the second PVC layer is a transparent layer. the componentsrequired are mixed in the following proportion:

EXAMPLE 4

[0035] The material according to Example 2 (thickness 1.5 mm without thecarbon-glass fiber layer, layer 1 according to FIG. 2) was adhered to a0.5 mm thick transparent layer (layer 3 according to FIG. 2), preparedas follows:

[0036] 100 parts of PVC, 55 parts of plasticizer (30 parts of DPOF and25 parts of aliphatic ester), 20 parts of filler (ATH) and 2 parts ofstabilizer. To the bottom of layer 1 illustrated by FIG. 2, a conductivecarbon-glass fiber layer was adhered which contains 10% of carbon fiber,and the resistivity of the material was measured across its thicknessaccording to the standard SFS-EN 100015, and the resistivity of 4×10⁶ Ωwas obtained.

[0037] Consequently, with use of suitable colours, it is possible toprint a desired pattern on the first PVC surface and then to cover itwith a second transparent PVC layer to obtain a semiconducting but, asto its appearance, a pleasant and appealing floor covering.

[0038] The conductive layer 2 may, as noted above, be formed of acarbon-glass fiber composition or by employing a wire mesh or the like.Further, the conductive layer may be obtained by printing, usingconductive printing inks, a separate conductive layer either below thefloor covering or, in case of a floor covering made of more than one PVClayers, between two layers. If desired, the conductive layer may also bemade of normal mass that contains carbon black, although it has itswell-known drawbacks. Furthermore, there may be provided a separatenon-conductive layer of covering below the floor covering if it isdesired to isolate the floor covering from its actual bedding. It isessential, however, that the PVC material extending from the surface ofthe floor covering to the conductive layer is prepared in the waysdisclosed above, so that, as to its resistive properties, the entirefloor covering is semiconducting.

[0039] Regarding the fillers, the talc may be pure talc or talcosematerial made from soap rock by grinding. However, when determining theparts of components in the covering material, they are determinedaccording to the amount of pure filler i.e. pure talc, and the additivesin the soap rock powder are not taken into account. The filler may beATH or talc, and if desired they may both be used simultaneously.Furthermore, DPOF and/or an aliphatic ester compound (such as theproduct sold by the trade name Bisoflex 124™) may serve as theplasticizer, or these two together, or either one of them blended intoone or more of the following plasticizers:

[0040] monomeric or polymeric phthalates

[0041] monomeric or polymeric adipates

[0042] phosphate plasticizers

[0043] polyester plasticizers

[0044] trimellitate plasticizers

[0045] alkylsulphonic acid esters

[0046] glycoates

[0047] benzoates.

[0048] PVC material prepared according to the invention may, if desired,also be foamed, with the covering layer produced still fulfilling therequirements of semiconductivity. In addition, the conductive layer maybe produced by a way known per se, in which the conductive layer isformed of material compounded from different kinds of conductiveparticles.

1. A semiconducting floor covering which consists of a layer (2) ofconductive material parallel to the surface of the covering and at leastone layer (1, 3) of polyvinyl chloride based material which is adheredto the layer of conductive material and which contains polyvinylchloride and at least one plasticizer, characterized in that theplasticizer at least mainly consists of 2-ethyl hexyl diphenyl phosphateand/or an aliphatic ester compound, and that the polyvinyl chloridematerial contains, as filler, talc and/or aluminium trihydrate so thatthe relative proportions of the components in the polyvinyl chloridematerial per 100 parts of polyvinyl chloride are 30-80 parts of saidplasticizer and 1-250 parts of said filler.
 2. A floor covering asclaimed in claim 1 , characterized in that the conductive layer is acarbon-glass fiber layer.
 3. A floor covering as claimed in claim 1 or 2, characterized by comprising at least one colourless layer wherein theproportions of the components are 100 parts of polyvinyl chloride, 35-70parts of plasticizer, and filler in such an amount that the proportionof pure talc and/or aluminium trihydrate therein is 1-90 parts.
 4. Afloor covering as claimed in claim 3 , characterized by comprising atleast one transparent polyvinyl chloride layer wherein the proportionsof the components of the polyvinyl chloride materials are 100 parts ofpolyvinyl chloride. 35-70 parts of plasticizer, and filler in such anamount that the proportion of pure talc and/or aluminium trihydratetherein is 1-90 parts.
 5. A floor covering as claimed in claim 3 or 4 ,characterized by comprising at least two layers of polyvinyl chloridematerial, whereby the lower layer adhered to the conductive layer iscoloured.
 6. A floor covering as claimed in claim 5 , characterized inthat a pattern has been printed on the surface of the coloured layerprior to forming the colourless or transparent layer.